When bulk materials such as ore, coal and stone are transferred from a chute or feeder to a belt conveyor, the belt tends to be damaged. Therefore, the chute or feeder is developed so as to lower the dropping energy onto the conveyor belt. For instance, a ladder or stone box L is mounted on the inside of the chute as shown in FIG. 11 so that the drop distance of bulk materials becomes shorter. Alternatively, the chute is usually designed with a throat portion and a pair of plates SC as the bulk materials tend to jump off the belt and lodge between carrier roller C and the belt B as shown in FIG. 12, in which R is a return roller.
The portion of the belt positioned where bulk materials are transferred from the chute is supported by plural carrier rollers C, spaced from each other, so that the dropping materials jump about on the belt and engage between the belt and the rollers C. In this manner, the belt tends to be damaged. Therefore, as shown in FIG. 13, it is proposed that the carrier roller is covered by rubber materials, the rollers are supported by rubber liners RL and also a carrier table T is supported by coil springs or an air cushion device SP. However, such remodeling is unwieldy and such a roller supporting system fails to alleviate dropping impact between the carrier rollers.
To avoid such problems, a proposed supporting arrangement for a belt conveyor comprises a top plate P, made of high molecular polyethylene, which comes into contact with a running belt and an elastic plate R, made of natural or synthetic rubber, through which the top plate P is mounted on a supporting frame so as to support the conveyor belt B on a lubricous surface of the top plate and absorb the dropping impact by the elastic plate P (Japanese Utility Model KOUKAI 137711/1985 and 190106/1988).
In such cases, however, there are some problems such that the top resin plate P becomes badly worn in a short time because it comes into constant surface contact with the running belt and thus the friction area is larger than that in a conventional roller supporting system, so that the resin plate tends to soften and wear out owing to friction heat. Furthermore, it is difficult to bend a resin plate having sufficient rigidity and thickness into the arc troughed shape, which is necessary to convey the bulk materials without excessive jumping on the belt surface. Therefore, as shown in FIG. 14, the resin plate is divided into at least 3 parts so that the belt enters into the opening D between the inclined support plates and the horizontal support plate and thus is worn away or cut down. In the worst cases, the supporting system itself is damaged. Besides, the dropping impact can be lessened only to a limited extent with the elastic plate, so that the dropping materials still tend to jump or flow out through the opening between the chute S and the belt B, causing sanitation problems. It is proposed, therefore, that the opening must be closed by a rubber skirt plate, but it is inevitable that the plates and belt are cut down and wear unevenly because the bulk materials such as ores enter into the small opening between the skirt and belt (which widens with abrasion).
Additionally, the bulk materials drop down from the chute onto the running belt at random, so that material cannot be loaded uniformly onto the receiving surface of the belt and thus the belt tends to run zigzag. Such zigzag running causes the belt to be worn locally. To avoid this problem, attempts have been made to adjust the tension of the endless belt by tension pulleys, but is is difficult to avoid zigzag running.